JP2012021938A - Cyclic saturated hydrocarbon compound detection element and optical detection device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cyclic saturated hydrocarbon compound detection element which operates at relatively low temperature of 200°C or less and a detection device using the same and having a simple structure.SOLUTION: A detection element has a transparent substrate made from quartz, a tungsten trioxide thin film having a columnar crystal structure on the transparent substrate, and a platinum layer deposited and formed on the thin film surface to have a thickness of 15 nm or less. A detection device has a heater for heating the detection element to the temperature of 150°C to 200°C and is constructed such that when gas containing cyclic saturated hydrocarbon compound comes into contact with the platinum layer of the detection element, the change of the light transmittance due to the reaction of hydrogen made free by the platinum with tungsten trioxide is measured.

Description

  The present invention relates to a sensing element for a cyclic saturated hydrocarbon compound that changes its light transmittance when exposed to an atmosphere containing the cyclic saturated hydrocarbon compound, and an optical system for detecting the cyclic saturated hydrocarbon compound using the same. The present invention relates to a detection device.

  The sensing element and the sensing device according to the present invention can be used not only in hydrogen storage plants and transport devices that use a large amount of cyclic saturated hydrocarbon compounds, but also in stationary dehydrogenation devices that supply hydrogen to household fuel cells, It can also be used to detect leakage in an on-vehicle dehydrogenation device for a fuel cell vehicle. In addition, it can also be used as a leak detection sensor that ensures the safety of the dehydrogenation device in all machines that use hydrogen, such as ships, trams, and boilers.

  As a means to safely store and transport hydrogen as a fuel for the realization of the hydrogen society as described above, organic hydrides that reversibly store and release hydrogen via platinum catalysts (such as cyclohexane and decalin) Cyclic saturated hydrocarbon compounds) are being researched and developed.

  Conventionally, as disclosed in Patent Document 1, most of the sensors that constantly detect flammable gas are of catalytic combustion type or heat conduction type, and the sensor requires a power circuit as an ignition source. It is. For this reason, an explosion-proof structure for avoiding the danger of ignition and explosion is required at the sensor installation location, and the sensor structure is complicated and heavy and expensive.

  Further, Patent Document 2 discloses a hydrogen gas sensing element having a structure similar to that of the cyclic saturated hydrocarbon compound sensing element of the present invention. This consists of a ceramic transparent substrate, a tungsten trioxide thin film formed by sputtering on the transparent substrate, and a catalytic metal layer such as platinum deposited on the thin film surface to a thickness of 30 to 50 nm. An optical hydrogen gas sensing element is shown. In Patent Document 2, molecular hydrogen gas is adsorbed by a catalytic metal, dissociates hydrogen atoms, and the dissociated hydrogen atoms are diffused into a tungsten trioxide thin film layer as an underlayer. As a result, the thin film layer is colored and the light transmittance is changed. Therefore, it is shown that the hydrogen gas concentration can be measured by measuring the light transmission intensity with the light receiving element.

JP 2005-207879 JP2007-121013

  Since cyclic saturated hydrocarbon compounds that are expected as a hydrogen transport and storage medium are volatile and flammable, it is essential to develop a detection method that ensures the safety by quickly detecting leaked and retained volatile components. .

  Accordingly, an object of the present invention is to provide a cyclic saturated hydrocarbon compound detection element capable of optically detecting a volatile organic hydride in a short time at a relatively low element temperature, and a detection apparatus using the same. There is.

  A sensing element for a cyclic saturated hydrocarbon compound according to one aspect of the present invention includes a transparent substrate made of ceramics such as quartz, a tungsten trioxide thin film having a columnar crystal structure on the transparent substrate, and a surface of the thin film. It consists of a platinum layer deposited to a thickness of 15 nm or less.

  An apparatus for detecting a cyclic saturated hydrocarbon compound according to another aspect of the present invention includes a transparent substrate made of ceramics such as quartz, a tungsten trioxide thin film having a columnar crystal structure on the transparent substrate, and a surface of the thin film of 15 nm or less. And a heater for heating the sensing element to a temperature between 150 ° C. and 200 ° C., comprising a sensing element of a cyclic saturated hydrocarbon compound comprising a platinum layer deposited to a thickness of A hollow heater through which light transmitted through the sensing element passes, and a housing that accommodates the heater and the sensing element, each having a gas inlet and a gas outlet and opposing each other constituting the housing Detection of a cyclic saturated hydrocarbon compound comprising a housing having a part of a surface made of a light transmitting member, a light source, and an optical measuring instrument including a light receiving element that receives light from the light source. The hydrogen gas dissociated by platinum when the gas containing the cyclic saturated hydrocarbon compound flowing in from the gas inlet is exhausted from the gas outlet while being in contact with the platinum layer of the sensing element. Is configured to measure a change in light transmittance caused by reacting with tungsten trioxide with the optical measuring instrument.

  As will be described in detail later, since the thickness of the platinum deposition layer is less than half of the conventional thickness, the light transmission intensity can be increased, and the signal intensity ratio (S / N) to the noise level can be improved. As a result, the gas containing the low-concentration cyclic saturated hydrocarbon compound can be detected in a short time after leakage.

It is a figure which shows an example of the detection element which concerns on this invention. It is a figure which shows an example of the detection apparatus which concerns on this invention. It is a schematic diagram which shows the basic principle of the detection element which concerns on this invention. It is an electron micrograph which shows the columnar crystal of platinum of the detection element which concerns on this invention. It is a figure which shows the result of the performance test according to gas concentration of the detection apparatus which concerns on this invention. It is a figure which shows the result of the performance test according to operating temperature of the detection apparatus which concerns on this invention.

  The present invention provides a sensing element for a cyclic saturated hydrocarbon compound composed of a tungsten trioxide thin film having a columnar crystal structure on a ceramic transparent substrate and platinum deposited on the thin film, and a sensing device using the same. To do. More specifically, the sensing element of the present invention is such that a platinum layer deposited on the surface of a tungsten trioxide layer deposited on a transparent substrate that transmits light in the visible to infrared range is used under heating conditions. It is configured.

  The structure of the sensing element of the present invention is shown in FIG. As shown in the sectional view shown in FIG. 1, this sensing element has a structure in which a platinum deposition layer 1, a tungsten trioxide layer 2, and a transparent substrate 3 are arranged in this order from the top to the bottom of the drawing. . The platinum deposition layer side becomes the cyclic saturated hydrocarbon compound detection surface. Next, an example of the manufacturing method of the sensing element of the present invention implemented by the inventors will be described.

  Using a high frequency sputtering method, a tungsten trioxide thin film was formed on the surface of a quartz substrate having a thickness of 1 mm. During film formation, metal tungsten was used as a target, and a tungsten metal target was sputtered at 50 W power for 1 hour in an argon gas partial pressure of 135 mPa and an oxygen partial pressure of 20 mPa. Tungsten trioxide was deposited on a quartz substrate at 600 ° C. The film thickness was about 300 nm. Thereafter, about 15 nm of platinum was deposited on the tungsten trioxide thin film using a high frequency sputtering method. Sputtering of platinum was performed by using platinum metal as a target, and sputtering for 40 seconds under the conditions of power 50 W and argon gas pressure 135 mPa.

  The cyclic saturated hydrocarbon compound to be measured by the sensing element of the present invention is typified by cyclobutane, cyclopentane, cyclohexane, methylcyclohexane, or decalin.

  Next, with reference to FIG. 2, the detection apparatus of the cyclic | annular saturated hydrocarbon compound concerning this invention is demonstrated. 10 is a sensing element of the cyclic saturated hydrocarbon compound described in FIG. 1, and 21 is a heater for heating the sensing element 10 to a temperature between 150 ° C. and 200 ° C. It has a hollow structure through which light transmitted through the sensing element 10 passes. A housing 31 accommodates the heater 21 and the detection element 10. The housing 31 has a gas inflow port 32 and a gas outflow port 33, and a part of mutually opposing surfaces constituting the housing is composed of a quartz window which is a light transmitting member. Reference numeral 41 denotes a red light source, and reference numeral 42 denotes an optical measuring instrument including a light receiving element that receives red light from the light source 41. These can use what is marketed normally. Here, for the test, nitrogen gas containing cyclohexane was used as the detection target gas.

  When the saturated saturated hydrocarbon compound-containing gas flowing in from the gas inlet 32 is exhausted from the gas outlet 33 while being in contact with the platinum layer 1 (see FIG. 1) of the sensing element, the ring is saturated with platinum. A change in light transmittance caused by the reaction of hydrogen dissociated from the hydrocarbon compound with tungsten trioxide is measured by the optical measuring instrument. FIG. 3 schematically shows the reaction between hydrogen and tungsten trioxide. This reaction is speculative and not experimentally confirmed. In order to help understanding of the present invention, an electron micrograph showing the crystal orientation (columnar structure) of the tungsten trioxide film is shown in FIG.

  According to the present invention, it has been found that cyclic saturated hydrocarbon compounds can be detected by heating a substrate composed of tungsten trioxide and platinum. The heating method is performed by a ceramic heater, but a light source such as an infrared ray or a pulse laser can be used as a heat source. Since the detection material containing tungsten trioxide as a main component can be formed by simply laminating it on the substrate surface, it can be easily manufactured.

The main component of the tungsten trioxide thin film is tungsten trioxide (W0 ₃ ), and the thickness is desirably 1 μm or less so that peeling does not occur from the transparent substrate. The tungsten trioxide thin film forms tungsten trioxide by depositing metallic tungsten on a transparent substrate such as quartz in an oxygen atmosphere. In the present invention, the tungsten trioxide film is deposited by the high frequency sputtering method, but a direct current sputtering method, a laser ablation method, a vacuum deposition method, a sol-gel method, or the like may be adopted. Further, platinum is deposited on the surface of the tungsten trioxide thin film using a high frequency sputtering method, but a direct current sputtering method, a laser ablation method, a vacuum deposition method, a sol-gel method, or the like may be employed.

  Hereinafter, a test example will be shown, and a detection element mainly composed of tungsten trioxide whose optical characteristics change when exposed to an atmosphere containing a cyclic saturated hydrocarbon compound and a detection method using the same will be described in detail.

Several characteristics tests of the sensing element according to this example were performed to confirm the performance.
<Test Example 1>

  Changes in the optical characteristics with respect to the gas containing the cyclic saturated hydrocarbon compound were evaluated at 200 ° C. using the measuring apparatus shown in FIG. Cyclohexane was used as the cyclic saturated hydrocarbon compound used for the evaluation, and cyclohexane having a concentration of 4.6% diluted with nitrogen gas was used. The sample in the cell in which the atmosphere and temperature can be controlled was irradiated with red light having a wavelength of 645 nm, and measurement was performed using a spectroscopic instrument in the following procedure.

(1) After the sample cell is purged with nitrogen for 5 minutes, the sample is heated to 200 ° C.
(2) The transmitted light intensity I ₀ of the sample before being exposed to cyclohexane is measured.
(3) A cyclohexane having a concentration of 4.6% diluted with nitrogen gas is passed through the sample cell at a flow rate of 50 ml / min.
(4) The transmitted light intensity I of the sample after passing through cyclohexane gas is measured.
(5) Change in light transmittance by cyclohexane was evaluated by I / I ₀ .

FIG. 5 (a) shows the time change of light transmittance by cyclohexane. It can be seen that the light transmittance decreases with increasing exposure time to cyclohexane gas, that is, the tungsten trioxide layer is colored. From this result, it can be seen that the cyclic saturated hydrocarbon compound can be sufficiently detected by observing the change in transmittance.
<Test Example 2>

In the present invention, it is important that cyclohexane can be detected even if it is below the lower explosion limit in air (1.8%). With respect to the sensing element according to this example, the time change of light transmittance with cyclohexane gas having a concentration of 1.1% at a flow rate of 200 ° C. and 50 ml / min was measured as in <Test Example 1>. The measurement result is shown in FIG. 5 (b). It can be confirmed that the light transmittance decreases as the exposure time of cyclohexane gas increases. Although the amount of change decreased compared with the case where the concentration of cyclohexane was 4.6%, it was possible to observe. From this result, it can be seen that detection is possible even when the concentration of cyclohexane is 1.1%.
<Test Example 3>

  In the present invention, the heating temperature of the substrate is important. Therefore, the change over time of the light transmittance of the sensing element according to the present embodiment with a cyclohexane gas having a concentration of 4.6% at a flow rate of 150 ° C. and a flow rate of 50 ml / min was measured as shown in <Test Example 1>.

The measurement results are shown in FIG. It can be confirmed that the light transmittance decreases as the exposure time of cyclohexane gas increases, but the amount of change is significantly smaller than that at 200 ° C (Fig. 6 (a)). From this result, it can be seen that the temperature of the detection material is important for the detection sensitivity.
[Comparative Example 1]

  In the present invention, platinum on the tungsten trioxide film is important. Therefore, as a comparative example of Example 1 described above, a tungsten trioxide thin film sample in which platinum was not deposited was prepared. The structure (not shown) of the detection element of Comparative Example 1 was the same as that of Example 1 described above except that the platinum deposition layer 1 was not formed.

  For Comparative Example 1 as well, the temporal change in light transmittance was evaluated under the same conditions as in Example 1. Although the results are not particularly shown, the transmittance by cyclohexane hardly changed in tungsten trioxide on which platinum was not deposited, and cyclohexane could not be detected. That is, when cyclohexane is detected using a tungsten trioxide film, it is an important item to deposit platinum on the tungsten trioxide film.

  From the above, when detecting a cyclic saturated hydrocarbon compound using a tungsten trioxide film, platinum is deposited on the tungsten trioxide film and used, and the substrate temperature is 150 ° C. to 200 ° C., Most preferably, it is set to 200 ° C.

  According to the present invention, it is possible to perform detection without involving a power supply circuit or an explosion-proof structure as an ignition source in the detection unit. Therefore, it can be used for a portable cyclic saturated hydrocarbon compound sensor, a leak detection system using an optical fiber, and the like. INDUSTRIAL APPLICABILITY The present invention can provide an optical cyclic saturated hydrocarbon compound detection element and detection device that ensure the safety that is indispensable for the next-generation hydrogen energy practical application technology.

1 ... Platinum deposit
2 ... Tungsten trioxide layer
3 ... Transparent substrate

Claims (5)

  A sensing element for a cyclic saturated hydrocarbon compound comprising a transparent substrate made of ceramic, a tungsten trioxide thin film having a columnar crystal structure on the transparent substrate, and a platinum layer deposited to a thickness of 15 nm or less on the thin film surface. A transparent substrate made of ceramic, a tungsten trioxide thin film having a columnar crystal structure on the transparent substrate, and a cyclic saturated hydrocarbon compound sensing element comprising a platinum layer deposited to a thickness of 15 nm or less on the thin film surface; ,
A heater for heating the sensing element to a temperature between 150 ° C. and 200 ° C., the heater having a hollow structure through which light transmitted through the sensing element passes through the heater,
A housing for housing the heater and the detection element, the housing having a gas inlet and a gas outlet, and a part of the opposing surfaces constituting the housing are formed of a light transmitting member;
An optical measuring instrument comprising a light source and a light receiving element that receives light from the light source;
An apparatus for detecting a cyclic saturated hydrocarbon compound comprising:
Hydrogen released from the cyclic saturated hydrocarbon compound by platinum when the gas containing the cyclic saturated hydrocarbon compound flowing in from the gas inlet is exhausted from the gas outlet while contacting the platinum layer of the sensing element. An apparatus for detecting a cyclic saturated hydrocarbon compound, wherein a change in light transmittance caused by reaction with tungsten trioxide is measured by the optical measuring instrument.   3. The cyclic saturated hydrocarbon compound detection device according to claim 2, wherein the tungsten trioxide film has a thickness of 1 μm or less.   A sensing element for a cyclic saturated hydrocarbon compound comprising a transparent substrate made of quartz, a tungsten trioxide thin film having a columnar crystal structure on the transparent substrate, and a platinum layer deposited to a thickness of 15 nm or less on the surface of the thin film.   5. The sensing element for a cyclic saturated hydrocarbon compound according to claim 4, wherein the tungsten trioxide film has a thickness of 1 μm or less.

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